Electrochromic metal oxide films conventionally used in electronic devices such as display elements, light modulation elements, etc. are generally formed by a vacuum evaporation method. However, the vacuum evaporation method has problems in that the production apparatus is expensive and the productivity is low. The methods are generally disadvantageous in mass productivity and simplicity and are not always an excellent method.
As a process for producing a thin film-form metal oxide by a coating method using an inexpensive production apparatus, there has been proposed a process called MOD (metallo-organic deposition) process wherein an organometallic compound is decomposed by heating and firing to thereby obtain the thin film of the corresponding metal oxide, as described, e.g., in JP-A-58-110444 and Chem. Mater., vol. 2, p. 484 (1990). The term "JP-A" as used herein means an "unexamined published Japanese patent application".
However, processes conventionally proposed are not fully satisfying with respect to an adhesion strength between a metal oxide film and a substrate, the uniformity of the film, productivity, the production cost, and the change in absorbance during color appearance of the electrochromic device.
The present invention has been accomplished with a view to solve problems associated with conventional processes.